solar panels with thermal store

[mickyg]

I've been thinking for a while about the real life benefits of this kind of set up and up until recently had never actually encountered it. It always seemed like a good idea as you get the benefit of heating and hot water from solar but I've been unable to find any realistic unbiased information about its economics. Does anyone actually have such installation and more importantly used it through the winter with any kind of measurable gain for heating??
I know that modern panels are able to gain from natural light not just direct sunlight but one wonders how much during the winter.
Also a (possibly big) problem? I noticed that when I created a demand the boiler fired up shortly after to reheat the loss in the store, which seems a bit silly as then the solar is then only keeping the store warm in standby mode and the boiler is then boosting the recovery. Is there any obvious solution to giving the solar a better chance to recover the store on its own without compromising performance?
I thought about a delay on the boiler demand but then in low solar gain periods it might affect performance.
Using the biggest store possible, or more than 1(space problems :/) might lessen the demand but doesn't exactly solve the problem....
can't think of anything else of the top of my head..

Any thoughts?

 

[Agile]

In the UK solar only provides some of the HW. The saving for the average family with two adults and two children is about £100-£150.

There can be a little heat gain during the winter but usually not much.

The best benefit is if you dont get get up very early.

There is no payback if you have a professionally installed system as the return on capital is about 1-2% ignoring servicing.

If you have a pressurised solar system then it needs servicing every year at a cost of about £100 so there is little financial benefit.

A drain back system is cheaper and does not need much maintenance but these are not usually sold by the big firms as there is less profit in them.

A solar system is a luxury with no real benefit apart from the feel good factor for those people who buy organic produce and have it delivered by those Occado vans which run on bio diesel ( which is not as green as it sounds! ).

Tony

 

[BigBurner]

If you have a pressurised solar system then it needs servicing every year at a cost of about £100 so there is little financial benefit.

Not so. G3 does not apply in many installations.

A solar system is a luxury with no real benefit apart from the feel good factor for those people who buy organic produce and have it delivered by those Occado vans which run on bio diesel ( which is not as green as it sounds! ).

Have you seen energy prices these days? A DIYed solar system will pay for itself soon enough.

 

[BigBurner]

Also a (possibly big) problem? I noticed that when I created a demand the boiler fired up shortly after to reheat the loss in the store, which seems a bit silly as then the solar is then only keeping the store warm in standby mode and the boiler is then boosting the recovery. Is there any obvious solution to giving the solar a better chance to recover the store on its own without compromising performance?

Solar thermal stores have only the bottom section with the flow and return to the panels connected, and no other connections from the boiler.

The solar section can get above say the setpoint of 70-75C and the heat will rise up. The store can get to around 95C, above the boilers temp and work fine. If it only gets below the boiler temp then the solar heated water floats up as the top section cools. Also the DHW return via plat heat exchanger can be very low in temp and this enters into the solar section. As long as there is a temp differential the solar system will work. Most of the time it will be pre-heating rather than fully heating he DHW.

See http://www.heatweb.com for an explanation and drawings.

 

[Agile]

Not so. G3 does not apply in many installations.

Have you seen energy prices these days? A DIYed solar system will pay for itself soon enough.

Its nothing to do with G3 ! If you did the solar installers course then you would have been taught that its essential for the protection of the system that its serviced every year to chjeck the condition and top up the strength of the antifreeze.

Thats not required for a drain back.

A DIY solar installation will give a return on capital of 4-6% but whilst that will cover the capital cost of the installation it will not provide a "pay back" if the notional interest and repayment of capital is taken into account. That needs about 15% return on capital after servicing costs.

To obtain a payback, the installation would have to cost about £700-£1100 or less. At the present cost of panels and tube and solar cylinders thats about a third of current costs.

A big saving can be made if an existing cylinder is used with a plate HE but that needs some experience to design it but it can often be done.

To make solar viable we need cheap drainback panels. I dont see why they cannot be made for about £200 each if anyone wanted to invest the capital and achieve a good sales volume.

Tony

 

[mickyg]

agile, I appreciate what you say about costs, but my question was really aimed at the operation of such a system. I'm 27 and It would be nice to think I can get by for the rest of career repairing and installing boilers, but with the way things are going I see it as a good idea to keep my eye on the ball so to speak in regards to new technologies and after seeing such system and experiencing its downfalls I was interested enough to ask...

BB, You didn't really answer my question, not surprisingly as you only know what you read, you have no real life experience. The answer could only possibly come from someone who might have this type of system, or installed or worked on it. I'm quite capable of looking up websites and looking at drawings. But as with most things in this business, theory and practice tend often to be very different things.

 

[Norcon]

mickyg wrote

Is there any obvious solution to giving the solar a better chance to recover the store on its own without compromising performance?

Not that I know off.
Have no experience with solar but a little with refrigeration heat recovery.
One of the obvious problems the engineers encountered was when the higher temperature heat emitters in the premises were turned on by staff this cancelled out the benefit of the heat recovery due to its lower operating temperature.
The only benefit was using the heat recovery early in the morning to boost space temperatures up from cold and when the outside temperature was high enough to allow the recovered heat to be beneficial without the need for the other heat source.

Its the same scenario with solar heating as far as I can see. Turn on the boiler and the solar energy is cancelled out.
But why would anyone spend huge amounts of money for such little gain with solar space heating ?.
Thats what baffles me.
Good insulation would be a far better investment and no maintainance.

 

[BigBurner]

BB, You didn't really answer my question, not surprisingly as you only know what you read, you have no real life experience.

Amazing! he doesn't know me or what I have done or not done. Your Q was answered.

The answer could only possibly come from someone who might have this type of system, or installed or worked on it. I'm quite capable of looking up websites and looking at drawings. But as with most things in this business, theory and practice tend often to be very different things.

You got the right explanation from me and from an implementation view too.

 

[BigBurner]

Its the same scenario with solar heating as far as I can see. Turn on the boiler and the solar energy is cancelled out.

Read my explanation. The bottom section of the store is reserved for solar heat storage. Only the DHW return entered this section as in most cases, when a plate heat X is used, the DHW temp is cool. The top boiler heated section may be hotter than the solar heated section. When the top section cools as heat is being extracted, the hotter bottom solar section's water rises into the top section.

If the solar section get very hot, say 90C, its heat will rise into the top boiler section. A store can operate just under boiling point without any adverse affects. You store the free heat.

But why would anyone spend huge amounts of money for such little gain with solar space heating ?.
Thats what baffles me.
Good insulation would be a far better investment and no maintainance.

You may be right, and insulation with draught proofing, must be the first line of attack in any home. However energy price hypes are making solar cost effective now.

Solar heat banks/thermal stores have been successfully used in combi preheating. A blending valve gives 55C water temp to the combi inlet to boost the flowrate too.. If below 55C the combi tops up. Electric backup too in the store. A DIYed solar heat bank can be easily and cheaply made, with advantages of higher combi flows, electric backup and free solar heat, probably most of your summer DHW too.

The Alpha FlowSmart does this but the blending valve is set to 30-35C, because the store is small.
http://www.alpha-boilers.co.uk/products/?id=7

The SolarSmart uses an unvented cylinder and a diverter valve set to 60C. This would be better using a heat bank using a plate heat X.

 

[Paul Barker]

micky g

If you are corgi go to combustion chamber and see my personal solar install as it unfolds and over coming years an account of performance.

In brief i am to install one or two 1000 litre stores.

To draw from them via immersed coils indirect hot water and indirect heating run entirely separately from the normal heating and hot water.

That entails a separate heating system and a diverter valve for the hot water system.

Ultimately UFH for solar would be desired but initially I shall use a pair of wet convector heaters i took out of some offices.

The aim being to always procure a benefit from ultraviolet whenever it is available during the winter. But where family comforts demand the alternative energy natural gas shall remain available as a separate system.

Time will tell.

The south facing roof pitches shall be arrayed with evac tubes to the full. Our south facing wall shall be turned into a Trombe Wall.

future plans may involve geothermal top up via economy 7 to heat the store.

Little by little.

 

[Paul Barker]

Ps I don't buy the collectors are now better bull.

The only reason i am using EVac tubes is cheapness lightness and hence as a diy situation the ability to take managable portions onto the roof bit by bit.

Basically these panels have become so cheap it is not worth fashioning your own flatplate collector noton grounds of better performance which I doubt but on grounds of effort.

 

[BigBurner]

micky g

If you are corgi go to combustion camber and see my personal solar install as it unfolds and over coming years an account of performance.

Put it on here. It is not gas related. Sounds interesting. People maybe can give you some input.

A full roof array, UFH and a large thermal store, sounds very good.

 

[ajstoneservices]

--------------------------------------------------------------------------------

In the UK solar only provides some of the HW. The saving for the average family with two adults and two children is about £100-£150.

There can be a little heat gain during the winter but usually not much.

The best benefit is if you dont get get up very early.

There is no payback if you have a professionally installed system as the return on capital is about 1-2% ignoring servicing.

If you have a pressurised solar system then it needs servicing every year at a cost of about £100 so there is little financial benefit.

A drain back system is cheaper and does not need much maintenance but these are not usually sold by the big firms as there is less profit in them.

A solar system is a luxury with no real benefit apart from the feel good factor for those people who buy organic produce and have it delivered by those Occado vans which run on bio diesel ( which is not as green as it sounds! ).

Tony

Seems to me the only bit you got right was your name and i'm not certain of that.

 

[Agile]

Seems to me the only bit you got right was your name and i'm not certain of that.

If you dont agree with anything that I have said then please give a reasoned argument to explain exactly how you disagree.

I expect that you have a vested interest in pretending that there is a payback from a professionally installed solar system !

I have no such interest and so I can say it as it is!

Tony

 

[Paul Barker]

So you are talking 3,500 litres. Is this the type of storage you think necesssary

Here are may two 1,000 litre stores arriving http://i194.photobucket.com/albums/z10/v1505guy/dsc00004.jpg

Food grade containers £145 the pair delivered.
Can withstand 110 degrees Celcius continuous, as they are not to be sealed they cannot get higher. A small amount of antifreese to kill legionella a silver spoon in each. All heat transfer indirect in and out using thethe old coils from copper domestic hot water cylinders which at todays scrap prices are costing £13 each on average.